一も二も無く[ichimonimonaku] unhesitatingly
一言二言[hitokotofutakoto] a word or two
一石二鳥[issekinichou] killing two birds with one stone
一二に及ばず[ichininioyobazu] right away
一姫二太郎[ichihimenitarou] It's good to have a girl first and then a boy

うり二つ[urifutatsu] as alike as two melons (two peas in a pod)
黄道十二宮[koudoujuunikyuu] twelve signs of the zodiac
二度[futatabi] again
最小二乗法[saishounijouhou] least-squares method
三十二分音符[sanjuunibuonpu] 32nd note

一曹[issou] master sergeant (JSDF)
１等軍曹[ittougunsou] sergeant first-class
軍曹[gunsou] sergeant
御曹子[onzoushi] son of a distinguished family
三曹[sansou] sergeant (JSDF)

３等軍曹[santougunsou] sergeant
児曹[jisou] children
重曹[juusou] baking soda
重炭酸曹達[juutansansouda] sodium bicarbonate
上級曹長[joukyuusouchou] sergeant major